Most current and nearly all past oil production methods leave as much as 50% of the original oil in place. Recent efforts to recover that oil remaining in the reservoirs have had considerable success. Among the more promising of the methods being used today is an enhanced oil recovery process referred to as a surfactant flood. This chemical method has brought with it some very difficult oil dehydration problems. These problems are the direct result of the chemicals used in the reservoir to improve the movement of the oil out of the reservoir rock and into the producing wells. In the normal water-flood phase of producing oil from the reservoir, much of the oil in place remains because of the high interfacial tension between the oil and water. The droplets of oil will not flow freely through the capillaries in the reservoir rock. To overcome this mobility problem, producers are adding surface active agents to the flooding fluids. These surface agents, called surfactants, reduce the interfacial tension between the oil and water. Stable micelles are formed between the oil and water and these micelles flow through the pores of the reservoir rock, moving the oil and water to the producing wells. The surfactant is the emulsifying agent and the presence of that surfactant in the produced fluids makes the subsequent oil and water separation very difficult in surface facilities. The very chemical features that produce success downhole makes the normal oil and water separation difficult. This is one of the problems that require new and different systems to accomplish the treatment of oil to make it salable and useful.
In field tests run by Shell Development Co. and reported in the December, 1977 Oil and Gas Journal, tracer response studied showed how much channeling of flow from the inlet to outlet occurs in the present separation devices used in oil and water separation processes. The hydraulic efficiency of large tanks used as oil and water separation devices proved to be very low, in the range of 5% or less. Because the separation of the oil and water is so difficult in the surfactant flood-produced fluids, good hydraulic efficiency is a must for the vessels used in the separation process. The system of the present invention offers a practical method of accomplishing oil and water separation in fluids produced by the surfactant flooding process. More broadly, the present invention enables the treatment of a large number of difficult-to-treat emulsions of secondary recovery, regardless of whether there is an element such as surfactant to be recovered and recycled.